The invention relates to an improved method of flow injection analysis and an apparatus for performing such analysis. More particularly, the invention involves a mixing chamber which is continuously variable in volume, where the volume of the chamber can be increased or decreased before, during or after the mixing or reaction step of flow injection analysis and where the volume change may be controlled by computer in response to analysis results to modify the analysis parameters for optimum desired results.
Quantitative analysis of chemical reactions, where an analyte solution is mixed with a reagent or carrier solution, is a useful tool in many disciplines, including the clinical, agricultural, pharmaceutical, environmental, chemical and medical fields. Various optical detection devices, such as spectrophotometers, fluorescence detectors, luminescence detectors, atomic absorption detectors, and electrochemical detection devices, such as devices to measure potential, voltage, charge or amperage, or any device which can measure either directly or indirectly a chemical or physical parameter of a chemical entity (i.e., the product or reaction result) are useful in providing important information regarding the analyte or the reaction product. It is scientifically beneficial to be able to successively test a number of such reaction samples under identical conditions in order to reduce sampling error. A basic technique to perform this repetitive analysis is through batch analysis, where multiple individual containers are used and the analyte and reagents are mixed in each container under identical conditions. This basic technique can be relatively slow, and requires the handling and cleaning of the many containers.
Since in many situations a large number of analyses of a given reaction are desirable, two techniques have been developed which provide for continuous analysis rather than discontinuous batch analysis of reactions between analytes and reagents. The first is known as continuous flow analysis (CFA) and the second is known as flow injection analysis (FIA). Each utilizes a tube as a conduit through which serial, successive samples are supplied, mixed and analyzed in a continuous process. In CFA, air bubbles are used to separate successive samples so that unwanted intermixing of adjacent samples is precluded. Mixing of the analyte and reagent to produce a reaction product sample for analysis is usually accomplished by providing a relatively long length of coiled tubing through which the samples pass, with mixing of the reagent and analyte occurring as a result of laminar flow, turbulent flow and/or diffusion effects from the tube walls and the action of the air bubbles. The individual samples are part of a continuously moving stream passing through the mixing and analytical apparatus, such that analysis of a large number of samples can be accomplished in reduced time. The FIA method is an improvement over the CFA method, in that the samples within the tube are not separated by air bubbles. Instead the reagent is provided as a continuous carrier solution pumped through the tube, with the analyte injected or introduced into the carrier fluid through a valving mechanism at spaced intervals prior to the mixing coil, with mixing and reaction of the analyte and reagent occurring primarily in the mixing coil. Typical mixing coils are composed of small internal diameter tubes, conventionally about 0.8 mm i.d., formed of Teflon or similar material, in lengths ranging from 0.5 to 4 meters, representing 0.25 to 2 mL in volume. The length and internal diameter of the tube, along with the flow rate, determines the amount and time for mixing and reaction prior to the sample reaching the detector apparatus. Mixing results from laminar flow effects due to transport of liquid in the cylindrical tube and diffusion effects due to the differential in concentration of the analyte and the reagent. Alternatively, the continuously supplied carrier solution may be an inert or neutral solution with both the reagent and the analyte introduced into the carrier stream prior to the mixing coil. With FIA, the equipment involved is simpler since there is no need to supply air bubbles to separate the samples.
While much research has gone into developing mixing and reaction chambers or devices with particular configurations to optimize sample peak height or sample throughput, i.e., peak width, for the particular analysis being performed, a limitation of batch, CFA and FIA methods is that the container, mixing coil or other mixing or reactor device is of fixed volume. This greatly limits the adaptability of the chosen analytical configuration. To vary the mixing volume, different containers must be substituted in the batch method and tubing of different lengths or different internal sizing must be substituted in the CFA and FIA methods--requiring stoppage of the analysis and manual disassembly and reassembly of the equipment. In many situations it is necessary or very desirable to experimentally determine the optimum mixing and reaction parameters for a given type of sample or for the particular detection analysis being performed on the sample, and the availability of a limited number of fixed volume containers or mixing coils limits the ability to obtain the optimum conditions, as well as requiring time consuming trial-and-error to find the best conditions. Obviously, this also requires the physical presence of a researcher to make the changes, such that altering the equipment remotely or by computer is impossible. A related limitation of the known analysis methods and equipment is that the volume of the mixer/reactor cannot be altered during the mixing/reaction step itself, that is, while the analyte and reagent are combining within the mixer/reactor.
Among other objects which will be apparent from the detailed disclosure to follow, it is an object of this invention to provide an improved method of continuous flow or flow injection analysis and a novel apparatus for performing this method wherein the volume of the mixing and reacting chamber is continuously variable such that any desired volume within the maximum and minimum volume limits of the system can be chosen, and such that the volume of the mixing and reacting chamber may be altered while the analyte and reagent are mixing and reacting. It is a further object to provide such a method and apparatus which may be controlled by a computer or microprocessor, or by remote signal, either in a predetermined manner or in response to the analytical data detected during an analysis run, such that variation in volume of the mixing and reaction chamber is automatic or based on the results of prior analytical runs. It is a further object to provide such a method and apparatus where individual or multiple signal or peak attributes for a sample for a particular detector device, such as shape, height, or width of a detected peak pattern, can be controlled and modified as desired, where change in volume does not require disassembly and reassembly of components of the system, where the volume of the mixing and reaction chamber can be static or dynamic during analysis, and where the analysis can be performed remotely with no requirement for the physical presence or interaction of a researcher or technician.